The present invention relates generally to computer systems and more particularly to the hierarchical watermarking of content that is distributed via a network.
A traditional watermark is a translucent design that is impressed on paper during manufacture of the paper. The traditional watermark is only visible when the paper is held to a light source. Digital watermarks have been developed as the digital equivalents of conventional watermarks. Digital watermarks are embedded in digital content, such as images or documents. Digital watermarks are created by modifying the bits within the digital content to embed codes without significantly modifying the content in which the watermarks are embedded.
Digital watermarks are available in two varieties: visible or invisible. Visible watermarks correspond with the traditional watermarks found on paper. Visible watermarks are usually used to make clear the origin or data but are rarely used to identify the destination of data. Invisible watermarks are invisible to anyone other than the original distributor of the image. Invisible watermarks should be hard to detect so as to allow the distributor to securely identify a recipient of content. Invisible watermarks should be configured so that they survive printing and scanning.
Parties have proposed the use of digital watermarks to protect the dissemination of copyrighted content on the Internet. In particular, when a copy of content is to be distributed, a digital watermark is first embedded in the content. If the party that receives the copy of the content subsequently makes illicit (i.e. unauthorized) copies of the content, the watermark is embedded in the subsequently generated copies. As such, there is proof that the party that received the content is the one that generated the illicit copies. Copyrighted content such as images, text, computer programs and other types of content may have digital watermarks embedded in them.
The above-described conventional approach of embedding digital watermarks to content may prove cumbersome for content that is in high demand. Each time that a party wishes to send a copy of the content to a requester, the party must generate a new digital watermark and embed the digital watermark in the copy of the content that is to be distributed to the requester. When thousands of requesters seek copies of the content, the generation and embedding of the watermarks may prove quite a burden. Such situations may arise, for example, with content such as images, web pages, documents, computer programs or even text that is distributed over the Internet.
The present invention provides an approach to hierarchical watermarking. The watermarking is hierarchical in that each level in a hierarchy of distributors distribute its own watermark in the content before passing the content on in the hierarchy. The content source may embed a digital watermark in content before the content is passed to a distributor. The digital watermark may identify the content source and the distributor via information embedded in the digital watermark. This first digital watermark discourages the distributor from generating illicit (i.e. unauthorized copies) of the content. The distributor then embeds a second digital watermark in the content whenever a client seeks a copy of the content. The second digital watermark contains information identifying the client. The second digital watermark provides protection against the client generating illicit copies of the content. The burden of creating the second digital watermark is not placed on the content source but rather is placed upon an intermediary (i.e. the distributor).
In accordance with one aspect of the present invention, a method is practiced in a system that has a content source for distributing a copy of content to a content consumer. An intermediary is provided between the content source and the content consumer. The intermediary embeds a second digital watermark in the content. A first digital watermark is already embedded in the content. The digital watermarks are not visible to parties other than the respective parties that embedded the digital watermarks. Thus, the intermediary can detect the digital watermark it embedded, and the content source can see the digital watermark that the content source embedded. The content is forwarded with the first and second digital watermarks to the content consumer from the intermediary. The content may take many forms including image data, text, audio data and computer program instructions.
In accordance with another aspect of the present invention, a method securely distributes content over a computer network. The content source is provided for furnishing content and a first digital watermark is embedded in the content at the content source. A copy of the content with a first digital watermark is forwarded from the content source to a proxy for distribution. When a customer requests a copy of the content, a second digital watermark is embedded in the content and the content with the first digital watermark and the second digital watermark is forwarded to the customer. The proxy may be but is not limited to, for example, a file transfer protocol (FTP) server, a mail server or a web server that distributes web pages.
In accordance with an additional aspect of the present invention, information is received at a distributor for distributing content from a content source to a customer. The information concerns a secret known to the content source and identification of the distributor. The information is used to generate a digital watermark at the distributor and the digital watermark is embedded in the content at the distributor. The content has another digital watermark embedded in it.
In accordance with a further aspect of the present invention, a method is practiced in a system having a content source for providing content and multiple content distributors for distributing the content to customers. For each of the distributors, a secret is identified. The secret is known to the content source and a value is calculated from the secret and from information identifying the distributor. The calculated value is forwarded to the distributor for use in embedding a digital watermark in content at the distributor.
In accordance with another aspect of the present invention, a computer system includes an interface with a content source for receiving content from the content source. The computer system also includes a digital watermark facility for embedding a digital watermark in the content that is received from the content source. The content contains another digital watermark embedded in it by the content source. The computer system additionally includes an interface with a client for forwarding the content with the digital watermarks to the client.